1. Field of the Invention
The present invention relates to a walking assistance device for assisting a user in walking.
2. Description of the Related Art
Conventionally, as a type of walking assistance device, there is known one including a trunk attachment portion which is attached to a user's trunk, a thigh attachment portion which is connected to the trunk attachment portion via a hip joint portion corresponding to a human hip joint and attached to a thigh of a user's leg, a crus attachment portion which is connected to the thigh attachment portion via a knee joint portion corresponding to a human knee joint and attached to the crus of the user's leg, and a foot attachment portion which is connected to the crus attachment portion via an ankle joint portion corresponding to a human ankle joint and attached to a user's foot, wherein a drive source for driving each of the joint portions is provided coaxially with the respective joint portion (refer to Japanese Patent Laid-Open No. 2003-220102, for example). This type of walking assistance device is capable of assisting the user in walking by applying an assist moment from the drive source for driving the hip joint portion to the user's thigh via the thigh attachment portion, applying an assist moment from the drive source for driving the knee joint portion to the user's crus via the crus attachment portion, and applying an assist moment from the drive source for driving the ankle joint portion to the user's foot via the foot attachment portion.
The above-mentioned conventional walking assistance device is capable of assisting all movements of the user's thigh, crus, and foot. However, the user experiences a considerably constrained feeling as the thigh and the crus are restrained by the thigh attachment portion and the crus attachment portion. In addition, it is necessary to provide the drive sources for driving the joint portions such as the hip joint portion, the knee joint portion, and the ankle joint portion, respectively, which increases the cost disadvantageously.
In order to solve the above disadvantages, it is conceivable to provide a walking assistance device including a load transmit portion; a foot attachment portion attached to the user's foot; a leg link connected to the load transmit portion via a first joint portion located at an upper end thereof and connected to the foot attachment portion via a second joint portion located at a lower end thereof, and having a middle third joint portion which operates in such a way that a distance between the first joint portion and the second joint portion is variable; a drive source to drive the third joint portion, wherein a force generated for the leg link from the third joint portion driven by the drive source is transferred to the user's trunk via the load transmit portion. According thereto, the walking assistance device can assist walking by alleviating the load on the user's leg by means of the force from the leg link transferred to the user's trunk via the load transmit portion. Furthermore, it is possible to relieve the user of the constrained feeling by making the leg link free from the user's leg.
Meanwhile, it is also necessary to provide a battery for the drive source in the walking assistance device. Generally, it is conceivable that the battery is housed in a back pack shouldered by the user. However, this solution resultantly impairs the alleviation effect on the constraint feeling of the user. Therefore, it is desirable to provide a walking assistance device including a drive source for a third joint portion and a battery for the drive source without being shouldered in a back pack by the user.
However, in the above-mentioned case, since the drive source and the battery are both heavy loads, when the user stands upright, divergence of the center of gravity of the drive source and the battery to either a forward direction or a backward direction with respect to a frontal plane (a plane which is vertical and parallel to a transverse direction) passing through the lower second joint portion of the leg link generates a forward or backward tilt moment to the leg link with respect to the second joint portion as the center, which causes a forward or backward pushing force applied to the load transmit portion. Further, the moment of inertia around the first joint portion of the leg link may become great according to the disposed height of the drive source and the battery, which thereby increases a load applied to the free leg due to the moment of inertia of the leg link when a free leg of the user (a leg whose foot is off from the ground) swings forward.